This invention relates to heat exchangers, and more particularly it deals with a heat exchanger of the cross-fin coil type.
In this type of heat exchanger, several proposals have hitherto been made to do work on the surface of each of the fins in various ways to provide improvements in the effects achieved by the fins in transferring heat between the fins and a gaseous heat exchange fluid, such as air. For example, there has been proposed a fin unit comprising a multiplicity of slit fins formed on a fin base plate, each slit fin comprising a fin provided by cutting a fin base plate and raising the material of the plate in bridge form by means of a press while leaving a slit in the base plate where the material has been removed.
Some disadvantages are associated with this type of heat exchanger of the prior art. In the slit fin unit, the slit fins are arranged such that their surfaces are disposed parallel to the direction in which a current of air flows between the slit fin units, so that the slit fins contribute little to rendering the air current turbulent in flow. Additionally limitations are placed on the air current flowing between the fin units by the fin base plate that accounts for the majority of the area and velocity and temperature boundary layers tend to develop on the fin base plate, with a result that the slit fin portions show a high heat transfer performance but the fin base plate is poor in heat transfer performance, particularly in portions of the fin base plate that remain between the slit fins. In applications where the slit fins have a uniform height, the problem is raised that the slit fins in the rear are low in heat exchange efficiency, because the slit fins in the rear are located on the downstream side of the slit fins in the front.
Japanese Patent Application Laid-Open Number 105194/80 (Toshio Hatada, et al.) provides improvements in a fin unit. The fin unit disclosed in this laid-open patent application comprises a multiplicity of fins arranged in stepped fasion with respect to the direction in which an air current flows. The fins are complex in shape and are of the so-called bridge type in which each fin is connected to the fin base plate only at its shorter sides. Thus the fin unit disclosed is not wholly satisfactory because it leaves something to be desired in strength due to the aforesaid construction.
When the fin unit of the prior art is used with an air cooler, condensation formed on the surface of the fin unit tends to turn into droplets of water which block the slits. When this phenomenon takes place, the heat transfer characteristics of the fin unit are greatly reduced. No means is provided to cope with this situation.